Getting active and cutting excess body fat are two of the best ways a woman can dramatically slash her breast cancer risk — the science is clear. However, obesity, along with genetics, contributes to just 30 percent of the breast cancer diagnoses women get every year. What isn't so clear is what causes the remaining 70 percent of cases. And a new report released by the Institute of Medicine (IOM) of the National Academies of Science may not provide much hope of definite answers any time soon.

The goal of the two-year-long study was to determine whether there is a strong link between breast cancer and environmental factors. Specifically, the panel of 15 cancer-research experts and nine members of the IOM looked at hormone therapies, hair dyes, flame retardants, plastic and canned food chemicals, heavy metals, different types of radiation, smoking and drinking tendencies, pesticides and industrial chemicals. Though the report authors recommend high-priority research on endocrine disruptors like bisphenol A(BPA), dioxins and flame retardants because of the "provocative, but as yet inconclusive" evidence of an association with breast cancer, they weren't able to say definitively that chemicals were culpable in causing the disease, citing a lack of reliable scientific literature.

But that doesn't mean the report was all bad news, says Julia Brody, PhD, executive director of the Silent Spring Institute, a nonprofit that investigates how the environment relates to breast cancer. "The Institute of Medicine, for the first time, is telling breast cancer doctors to pay attention to chemicals that, in experimental studies, show biological activity that provides a plausible link to breast cancer," she says, adding that, as part of the report, the panel outlined a strong research agenda and called for better safety testing of those chemicals.

Furthermore, just because researchers didn't come up with a definitive answer doesn't mean the chemicals in question are safe. "The data on suspect chemicals like BPA or parabens isn't as complete as we would like it to be," explains Alexandra Scranton, director of science and research at Women's Voices for the Earth, a nonprofit group that works to eliminate toxic chemicals that impact women's health. But that's partly due to the fact that lax chemical regulation has allowed most of the 40,000-plus chemicals in existence today to be released onto the market before they've been tested for long-term health effects.

The onus shouldn't rest entirely on an individual woman to reduce her breast cancer risk, Scranton adds — products we use every day should be safe. "Individuals cannot shop their way out of the problem, nor should they be expected to reduce their risk all on their own," she says. "We need collaboration from government regulatory bodies, industry partners, and the medical community to work together to reduce environmental risks as a society."

"The report calls attention to the need for chemical safety testing," adds Brody. "We can't intentionally expose people to these pollutants in experiments and then wait 60 years to see what happens." And the sooner that safety testing comes, the better. A growing body of research suggests that the most important environmental exposures leading to breast cancer may be happening while you are still a fetus — when breast development is at its earliest stages. "What your body is exposed to in utero can alter the course of your breast development, making you more susceptible to breast cancer in later life," explains Scranton. "Many recent studies on environmental exposures look at women's exposures to chemicals as adults, which may not be playing as significant role as much earlier exposures." She says one exciting aspect of this new report is the call for breast cancer causes "across the life course," which would prioritize research for in utero exposures.

An estimated 230,000 women will be diagnosed with invasive breast cancer in 2011. Although treatment for the disease has come a long way — death rates have fallen by more than 30 percent since 1990 — prevention has not. Despite the lack of evidence linking chemicals and other environmental contaminants to the disease, there are science-based ways to protect yourself.

Employ these precautions based on strong evidence that they reduce breast cancer risk:

1. Maintain a healthy weight. Eating poorly and a lack of exercise can lead to added pounds, which can in term fuel estrogen levels in the body, a known risk factor for the most common forms of breast cancer.

3. Avoid excess medical radiation. Some medical tests use ionizing radiation which is linked to cancer. The study authors say don't avoid mammograms because the dose is so low, but only get higher radiation-emitting tests, such as CT scans, if absolutely necessary.

4. Watch what you drink. Drinking alcohol can cut heart disease risk, but if you drink too much, you could be bumping up your breast cancer risk. Eliminate drinking alcohol, or opt to have just one less than three times a week to cut your breast cancer risk.

Practice the precautionary principle for exposures about which there are still a lot of questions:

6. Clean greener. Most cleaning products on the market are laced with harmful industrial ingredients you won't find listed on the label. A 2010 study published in the journal Environmental Health found that many household cleaning products are actually smudging our health. In the study, breast cancer was twice as prevalent in women who used the highest amounts of cleaning products; those who used air fresheners and mold and mildew products (especially the ones containing bleach) faced the highest risk of being diagnosed with breast cancer. To detoxify your cleaning routine while still killing germs, read this.

7. Eat organic. Many studies are finding links between pesticide exposure and ADHD, autism, Parkinson's disease and cancer, including breast cancer. Because people are also exposed to many other different chemicals, it's hard for scientists to definitively say that certain pesticides cause cancer before the chemical's been on the market for decades. When you buy organic food, you're ensuring that your food is grown without chemical pesticides and fertilizers, sewage sludge laced with human and industrial waste, and genetically engineered ingredients.

8. Avoid canned food. Researchers may not have completely ID'd BPA as a breast cancer causer in humans, but we already know it causes mammary tumors in rodent studies. To lower your exposure to BPA, avoid canned food and choose fresh or frozen whenever possible.

9. Be mindful of mileage and the contents of your garage. Researchers involved with this report put a big emphasis on benzene's potential role in causing breast cancer. This volatile chemical vapors off as you pump gas and inhale air pollution from vehicles. Brody suggests getting an electric vehicle, taking public transportation, or driving the most fuel-efficient car you can afford to cut back on lifetime exposure. Be sure to avoid running your car inside a garage, and don't store gas-powered equipment like mowers or leaf blowers in your basement or a garage that's attached to your home — benzene vapors will find their way into your living space.

10. Avoid air fresheners and scented candles. You might be surprised to know that benzene often spews from artificially scented candles, creating major indoor air pollution. Choose beeswax candles and instead of using air fresheners that often contain carcinogens, clean up the source of the bad smell, and then put out a bowl of white vinegar to safety disperse any lingering aroma.